The purpose of nanotechnology and science is to understand, control and manipulate objects of a few nanometers in size. These nano-objects are known to behave as an intermediate between single atoms and molecules and bulk matter. These properties are often peculiar and different from the properties of bulk material; in particular, these nano-objects can present properties that vary dramatically with size. This opens the possibility of controlling these properties by precisely controlling their formulation process.
Nanoclusters are aggregates of atoms or molecules with an average diameter less than 100 nm and a number of constituent components ranging from 10 to 106. Nanoclusters do not have a fixed size, structure, or composition. As a result, they present a variety of morphologies. Nanoclusters may be homogeneous, which means composed of only one type of atom or molecule, or heterogeneous. The components within a nanocluster may be held together by very different kinds of forces, such as electro-static, Van der Waals, or covalent bonds, depending on the constituent. Small clusters of metal atoms, such as Cu (copper), are held together by forces more like those of covalent bonds, not like the forces exerted by the nearly free electrons of bulk metals. Clusters containing no more than a few hundred metal atoms, resulting in diameters around 3-5 nanometers, have strong, size-dependent properties due to quantum confinement. As the cluster becomes larger, with diameters up to 100 nanometers, they possess smooth variations of behavior approaching the bulk size limit.
Nanoclusters usually do not have a crystal lattice structure like their bulk counterparts. These finite clusters can present multiple nanocrystalline structures such as multiple hedronic structures with multiple faces. Some nanoclusters may be a crystalline solid. It is important to understand whether crystalline or noncrystalline structures prevail for a given size and composition in order to describe some physical process involving the nanocluster.
An interesting inquiry for consideration is what happens in a phase transition situation, like copper from liquid to solid, when there are nanoclusters. An answer to this question provides that thermodynamic and kinetic energy stabilities influence. Nanoclusters have a very high surface area to volume ratio resulting in a high surface energy. The nanocluster's structure, including facets, edges and vertices, has a strong influence to this surface energy and thus dominates the nanoparticle's behavior.
In order to fully understand the physical behavior of these nanoclusters several steps are taken. First, nanoparticle structure is the starting point for understanding copper nanocluster behavior. In order to gain a very complicated understanding of the structure-property relationship, a deep study of the minimum energetic situations was performed and the results analyzed. These results are very complicated and convoluted and, until now, have not been done by anyone in the world for copper nanoclusters. Second, is to determine the effect of increased temperature. To answer this question, one must be an expert in the thermodynamics of finite systems. There are very few experts in the world. Third, one needs to understand, in particular for phase transition of copper nanoclusters, what is the time scale in the experimental setting vs. the time scale of morphology transitions. Basically, this is solved by the study of kinetic effects in the formation and destruction of nanoclusters.